Condensing method



March 9, 1943. D. K. DEAN CONDENSINGMETHOD Filed oct. 25, 1958 PatentedMar. .i943

CONDEN SING METHOD Application october 25, 193s, serai No. 236,861

' (ci. 25a- 51) 1 Claim.

My invention relates to surface condensing systems which areparticularly useful in connection with paper mill pulp digester systems,although the invention is capable of more general applican tion. Moreparticularly, the invention pertains to a novel method for the recoveryof heat by the condensation oi condensible vapors having lsolidparticles entrained therein.

In paper mill digesters, it is customary to heat the sulphate or sodapulp, which consists largely of water, to temperatures of 300 Fiorhigher, with the result that the pressure within the digester willapproximately correspond to the pressure of water vapor at a saturationtemperature corresponding to the temperature of the liquid in thedigester. It is common practice in many mills, at the end of the cookingperiod, to dis.

charge the pulp, while at the maximum cooking pressure directly into ablow-down tank which is ordinarily under atmospheric pressure. As aresult of this sudden reduction in pressure, a large amount ofevaporation or flashing takes place and the heat of the enormousquantities of vapor and made use of in heating water or for otherdensers of the conventional type have been so y.

employed, they have proved generally ineective, due to accumulations ofpulp that have been entrained by the steam and driven into the tubebundle and onto the condensing surfaces during condensation, thusmaterially decreasing the etliciency of the apparatus.

Accordingly, it is the object of this invention to provide a method ofheat recovery which is arranged to overcome the above mentioneddisadvantages and to prevent solid particles from adharing to the tubesof the surface condenser, or otherwise aiecting its eicient operation.

The particular features and advantages that characterize my inventionwill be clearly under- Like reference characters refer to the same partsthroughout the several views.

Referring to the drawing, reference character l0 designates a blow-downtank which receives the pulp contents from a digester, not shown,through a tangential connection ll. From the upper portion of theblow-down tank l0 a conduit l2 leads to a cyclone-type separator I3, aconduit It returns separated pulp or other solid material from theseparator to the lower portion of the blow-down tank, and a vapor linei5 leads from the upper portion of the separator to a steam inletconnection l5, which enters the lower wall of a large vapor distributingor expansion chamber il, formed as shown, by continuing the walls ofshell i8 of a condenser i@ operated in accordance with the invention,for the greater part of the length of the shell, downwardly to a pointmaterially below the condensing tubes 20. A hood or impingement bae 2lextends over the discharge end of the inlet connection i6 and is spacedtherefrom and supported by strips 22. 0n either side of the inletconnection and adjacent the ends oi the expansion chamber il, arecondensate drain connections 23 and 24. The condensing tubes 20 aresupported within the shell I8 -by a xed tube sheet 25 at one end, and bya iioating tube sheet 26 at the other end to which a cover plate 2l issuitably secured. A. water box 28, provided with cooling water inlet andoutlet nozzles 29 and 30 respectively, is suitably secured to thestationary tube sheet end of the shell, and by means of a diaphragm 3lthe cooling water iiows through the condensing tubes in two passes. Atthe oating head end of the tube bundle the shell is closed by a shellcover plate 32. Non-condensible gases are released from the top of thecondenser by outlets 33 and 313 which are large enough to alsoadequately release the entire volume of steam in case the Water supplyshould fail. Such vapors are either vented to atmosphere, or to adisposal system, not shown, by conduit 35. The condensing o5 tubes aresupported intermediate their ends by spaced support plates 36 and 31. Aperforated pipe 38, which connects with a water supply, not shown,extends for substantially the full length of the tube bundle within thespace between the upper wall of the shell and the top row of tubes.

In operation, steam which is periodically released from the digestersystem and flashed off in the blow-down tank, flows from the separatorI3 together with non-condensible vaporsv and particles of entrained pulpthat were not removed from the vapor stream in the separator, throughthe conduit I5 to the condenser inlet in the large vapor distributingchamber I1 wherein a further expansion takes place, resulting in asubstantial reduction in the velocity of the vapors before they enterthe condensing surface of the tube bundle. produced, tends to eliminatea portion of the entrained pulp particles, and any particles not soeliminated from the vapor stream will ordinarily be knocked down by thecontinuous rain of condensate descending from the tube surfaces. Di--The relatively low vapor velocitfthus rect impingement of the enteringvapor and solids on the condensing surface is prevented by means of thebaille 2I, which also prevents the rain of condensate from entering thesteam inlet connection I6. Furthermore, in this connection, it will benoted that since the walls of the inlet connection extend a substantialdistance above the bottom of the chamber I1, normally all the condensateand any pulp carried thereby must pass through the drain connections 23and 25 and cannot enter the inlet connection I6. Since the water box 28is so arranged that the cooling water flows in two passes, first throughthe tubes of the upper portion of the condensing surface, and thenthrough the tubes of the lower portion thereof, the cooling water' iiowscounter-current to the flow of the steam.

As already referred to, the velocity of the steam is so reduced onentering the condenser, that very little, if any, pulp will be carriedby the steam from the distributingY chamber upwardly into the tubebundle. However, the steady downward flow of condensate duringcondensation serves as a continuous wash for the tube surfaces andeffectively prevents the possible accumulation of any pulp thereon.Obviously the effectiveness of the condensing surface and the washingeffect of the condensate is augmented by the counter-current flow ofcooling water and steam.

At times when the system is shut down, the entire tube bundle and thelanes between the condenser shell and the tube bundle may, if desired,be thoroughly scoured and washed down by water which may be dischargedfrom the perforated water pipe 38.

It will be apparent, that by utilizing the invention, steam containingsolid material and other impurities resulting from a sulphate or sodapulp cooking process, or other similar processes, may be readily andeconomically condensed in a surface type condenser, thereby recoveringthe heat `of the vapors, which is imparted' to the condenser coolingwater, and thus provides a useful source of uncontaminated heated water.

Quite apparently, the principles of the invention may be employed torecover heat from con. densible vapors other than steam, in which solidmaterial is entrained.

Since certain changes may be made in the specic form and arrangement ofthe apparatus disclosed without departing from the principles of theinvention, it is to be understood that no intention is entertained tolimit the invention except by the scope of the appended claim.

What I claim is:

In the method of recovering heat from the vapor of pulp digesterblowdown, the steps of introducing the vapor and entrained pulp into thelower portion of a condensing zone, flowing the vapor and entrained pulpupwardly over a condensing surface, and withdrawing condensate from saidzone, the operation being such that condensateof the vapor flowsdownwardly over said condensing surface and prevents the accumulationthereon of the pulp entrained in the vapor flowing over said surface.

DION K. DEAN.

